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  • richardmitnick 3:43 pm on June 22, 2017 Permalink | Reply
    Tags: Africa, Charting a better future for Africa, Charting a better future for Africa under uncertainty, Engineering sustainable development and poverty reduction, MIT   

    From MIT: “Charting a better future for Africa” 

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    June 22, 2017
    Mark Dwortzan | MIT Joint Program on the Science and Policy of Global Change

    1
    Joint Program on the Science and Policy of Global Change Research Scientist Kenneth Strzepek meets with Ethiopian Minister of Agriculture Tefera Deribew. Photo: Brent Boehlert

    Almost 25 percent of the world’s malnourished population lives in sub-Saharan Africa (SSA), where more than 300 million people depend on maize (corn) for much of their diet. The most widely-produced crop by harvested area in SSA, maize is also highly sensitive to drought. Because maize in this region is grown largely on rainfed rather than irrigated land, any future changes in precipitation patterns due to climate change could significantly impact crop yields. Assessing the likely magnitude and locations of such yield changes in the coming decades will be critical for decision makers seeking to help their nations and regions adapt to climate change and minimize threats to food security and to rural economies that are heavily dependent on agriculture.

    Toward that end, a team of five researchers at the MIT Joint Program on the Science and Policy of Global Change and the Department of Earth, Atmospheric and Planetary Sciences (EAPS) has applied a broad range of multi- and individual climate model ensembles and crop models to project climate-related changes to maize yields in Africa throughout most of the 21st century. Accounting for uncertainty in climate model parameters — which is most pronounced in high-producing semiarid zones — the researchers project widespread yield losses in the Sahel region and Southern Africa, insignificant change in Central Africa, and sub-regional increases in East Africa and at the southern tip of the continent. The wide range of results highlights a need for risk management strategies that are robust and adaptive to uncertainty, such as the diversification of rural economies beyond the agricultural sector.

    “In the wet regions you’d feel very secure in making large-scale, long-term agricultural decisions, knowing that the probability of error due to climate change is small,” says Joint Program Research Scientist Kenneth Strzepek, one of the study’s principal co-investigators (the other is Susan Solomon, the Lee and Geraldine Martin Professor of Environmental Studies in the EAPS Department). “In the arid regions, where the magnitude of uncertainty is much higher, you’d need to proceed with caution. That means developing strategies that hedge on which crops are cultivated, learning more about how the climate is changing before making any major investments, and considering alternatives to agriculture for economic development.”

    The study was published in March in the journal AGU Earth’s Future and was funded by the Abdul Latif Jameel World Water and Food Security Lab and supported in-kind by the World Bank. It is right in Strzepek’s wheelhouse. For more than 40 years, he has cultivated expertise in environmental science and economics and applied it to promote sustainable development and poverty reduction, with an emphasis on optimizing the use of water resources in the developing world.

    Engineering sustainable development and poverty reduction

    Inspired by the creation of the Environmental Protection Agency in 1972, Strzepek started out pursuing a bachelor’s degree in environmental engineering at MIT, with the ultimate goal of working on U.S. environmental concerns. But during the summer of his sophomore year, after contracting a waterborne disease while participating in a water supply project in Mali, he felt called to shift his focus to the interplay of poverty, development, and public health. Propelled by this experience and the tenets of his Christian faith, he resolved to apply his engineering skill set to help alleviate poverty and promote sustainable economic development in resource-limited countries.

    To enhance his effectiveness in carrying out this mission, he spent the next eight years at MIT earning BS and MS degrees in civil engineering and a PhD in water resources systems analysis. He also completed an MA in economics from the University of Colorado (where he also served as a professor of civil, environmental, and architectural engineering); and now, as a true lifelong learner, is midway through a PhD program in economics at the University of Hamburg in Germany. Anchored by this interdisciplinary academic background, he has spent his career working at the intersection of water, agriculture, environmental, and economic policy, modeling these systems to understand their linkages and implications for investment and policymaking in both developing and developed regions.

    Today Strzepek splits his time three ways. First, as a research scientist at the MIT Joint Program he churns out peer-reviewed papers, such as the Earth’s Future study, that explore impacts of climate change on natural resources and economic development. As an educator, he serves as an adjunct professor of public policy at Harvard University’s John F. Kennedy School of Government focused on water and climate policy and as an adjunct faculty member at Denver Seminary in Colorado, where he teaches a course on development and poverty. Finally, as a consultant for the U.S. government, the World Bank, and the United Nations, he works on projects focused on sustainable development and poverty reduction.

    For the U.S. Environmental Protection Agency, Strzepek has contributed to the 2015 Climate Change Impacts and Risk Analysis (CIRA) report, which estimated the environmental and economic benefits to the U.S. of reducing global greenhouse gas emissions. For the World Bank, he has helped develop a comprehensive framework agreement between all sovereign states in the Nile River basin to cooperatively manage their shared water resource. And as a nonresidential senior research fellow at the U.N. University World Institute for Development Economics Research (UNU-WIDER), he helps lead a research project Development under Climate Change (DUCC), which examines the impact of climate change on water resources, agriculture, and other infrastructure systems, and the consequences for economic development in Africa and other developing regions. He is also a contributor to a Joint Program/UNU-WIDER project called Africa Energy Futures, which is exploring the potential economic benefits of shifting the continent’s energy system from fossil fuels to renewables.

    “Ken Strzepek is never one to lose the forest for the trees,” says Channing Arndt, another senior research fellow at UNU-WIDER. “Whether engaging in politically sensitive analysis of the Nile River or assessing the development implications of climate change, he has an uncanny ability to get to the crux of the issue. His many contributions include more realistic views of the implications of climate change in Southern Africa.”

    Raffaello Cervigni, a lead environmental economist with the World Bank’s Environment and Natural Resources Global Practice, also praises Strzepek’s approach.

    “Ken combines three traits that make him particularly effective in development work — world-class academic accomplishments, unbounded energy for Africans, and the right dose of humility,” says Cervigni, who has led several World Bank assignments in Africa in which Strzepek served as a lead consultant or technical advisor. “This combination means he is almost uniquely able to fully engage his developing country counterparts.”

    Charting a better future for Africa under uncertainty

    As he works to reduce poverty and expand sustainable economic development in Africa, Strzepek aims to ensure that nations in the region don’t either overreact or underreact to climate change. To assess the economic implications of such reactions, he considers the opportunity costs of policies designed to mitigate or adapt to climate change, i.e., what critical economic development projects, from new schools to housing, could have been funded if such policies were not implemented.

    Of particular interest to Strzepek is determining the role of agricultural development in ensuring food security and as a potential engine of economic growth across the continent, all while the magnitude, pace, and impacts of temperature and precipitation change remain uncertain.

    “Policymakers and investors are asking: How do we proceed with all of this uncertainty?” says Strzepek. “The Earth’s Future paper is one of the first attempts to try to see if there are any regions of Africa where the level of uncertainty is lower than we might expect. Using different climate models and accounting for variables that range from temperature to soil nutrient levels, is there a consistent signal that can direct decision-makers on how to proceed in the near future? We believe that our findings, which quantify the level of uncertainty by region, can help guide that process now.”

    See the full article here .

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  • richardmitnick 7:12 pm on June 19, 2017 Permalink | Reply
    Tags: , , Chromosomes, , MIT   

    From MIT: “How cells combat chromosome imbalance” 

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    June 19, 2017
    Anne Trafton

    1
    Chromosome segregation errors lead to abnormal karyotypes, a condition known as aneuploidy. Shown here is a cell undergoing cell division and experiencing chromosome mis-segregation. Courtesy of the researchers

    Biologists discover the immune system can eliminate cells with too many or too few chromosomes.

    Most living cells have a defined number of chromosomes: Human cells, for example, have 23 pairs. As cells divide, they can make errors that lead to a gain or loss of chromosomes, which is usually very harmful.

    For the first time, MIT biologists have now identified a mechanism that the immune system uses to eliminate these genetically imbalanced cells from the body. Almost immediately after gaining or losing chromosomes, cells send out signals that recruit immune cells called natural killer cells, which destroy the abnormal cells.

    The findings raise the possibility of harnessing this system to kill cancer cells, which nearly always have too many or too few chromosomes.

    “If we can re-activate this immune recognition system, that would be a really good way of getting rid of cancer cells,” says Angelika Amon, the Kathleen and Curtis Marble Professor in Cancer Research in MIT’s Department of Biology, a member of the Koch Institute for Integrative Cancer Research, and the senior author of the study.

    Stefano Santaguida, a research scientist at the Koch Institute, is the lead author of the paper, which appears in the June 19 issue of Developmental Cell.

    A downward spiral

    Before a cell divides, its chromosomes replicate and then line up in the middle of the cell. As the cell divides into two daughter cells, half of the chromosomes are pulled into each cell. If these chromosomes fail to separate properly, the process leads to an imbalanced number of chromosomes in the daughter cells — a state known as aneuploidy.

    When aneuploidy occurs in embryonic cells, it is almost always fatal to the organism. For human embryos, extra copies of any chromosome are lethal, with the exceptions of chromosome 21, which produces Down syndrome; chromosomes 13 and 18, which lead to developmental disorders known as Patau and Edwards syndromes; and the X and Y sex chromosomes, extra copies of which may cause various disorders but are not usually lethal.

    In recent years, Amon’s lab has been exploring an apparent paradox of aneuploidy: When normal adult cells become aneuploid, it impairs their ability to survive and proliferate; however, cancer cells, which are nearly all aneuploid, can grow uncontrollably.

    “Aneuploidy is highly detrimental in most cells. However, aneuploidy is highly associated with cancer, which is characterized by upregulated growth. So, a very important question is: If aneuploidy hampers cell proliferation, why are the vast majority of tumors aneuploid?” Santaguida says.

    To try to answer that question, the researchers wanted to find out more about how aneuploidy affects cells. Over the past few years, Santaguida and Amon have been studying what happens to cells immediately after they experience a mis-segregation of chromosomes, leading to imbalanced daughter cells.

    In the new study, they investigated the effects of this imbalance on the cell division cycle by interfering with the process of proper chromosome attachment to the spindle, the structure that holds chromosomes in place at the cell’s equator before division. This interference leads some chromosomes to lag behind and get shuffled into the two daughter cells.

    The researchers found that after the cells underwent their first division, in which some of the chromosomes were unevenly distributed, they soon initiated another cell division, which produced even more chromosome imbalance, as well as significant DNA damage. Eventually, the cells stopped dividing altogether.

    “These cells are in a downward spiral where they start out with a little bit of genomic mess, and it just gets worse and worse,” Amon says.

    “This paper very convincingly and clearly shows that when chromosomes are lost or gained, initially cells can’t tell if their chromosomes have mis-segregated,” says David Pellman, a professor of pediatric oncology at Dana-Farber Cancer Institute who was not involved in the study. “Instead, the imbalance of chromosomes leads to cellular defects and an imbalance of proteins and genes that can significantly disrupt DNA replication and cause further damage to the chromosomes.”

    Targeting aneuploidy

    As genetic errors accumulate, aneuploid cells eventually become too unstable to keep dividing. In this senescent state, they start producing inflammation-inducing molecules such as cytokines. When the researchers exposed these cells to immune cells called natural killer cells, the natural killer cells destroyed most of the aneuploid cells.

    “For the first time, we are witnessing a mechanism that might provide a clearance of cells with imbalanced chromosome numbers,” Santaguida says.

    In future studies, the researchers hope to determine more precisely how aneuploid cells attract natural killer cells, and to find out whether other immune cells are involved in clearing aneuploid cells. They would also like to figure out how tumor cells are able to evade this immune clearance, and whether it may be possible to restart the process in patients with cancer, since about 90 percent of solid tumors and 75 percent of blood cancers are aneuploid.

    “At some point, cancer cells, which are highly aneuploid, are able to evade this immune surveillance,” Amon says. “We have really no understanding of how that works. If we can figure this out, that probably has tremendous therapeutic implications, given the fact that virtually all cancers are aneuploid.”

    The research was funded, in part, by the National Institutes of Health, the Kathy and Curt Marble Cancer Research Fund, the American Italian Cancer Foundation, a Fellowship in Cancer Research from Marie Curie Actions, the Italian Association for Cancer Research, and a Koch Institute Quinquennial Cancer Research Fellowship.

    See the full article here .

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  • richardmitnick 2:18 pm on May 31, 2017 Permalink | Reply
    Tags: , , MIT, MIT’s Department of Nuclear Science and Engineering (NSE), Zach Hartwig   

    From M.I.T.- “Zach Hartwig: Applying diverse skills in pursuit of a fusion breakthrough” 

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    May 22, 2017
    Peter Dunn
    Department of Nuclear Science and Engineering

    1
    Assistant Professor Zach Hartwig joined the Department of Nuclear Science and Engineering faculty this year after almost a decade of doctoral and postdoc work at MIT. Photo: Lillie Paquette/MIT School of Engineering.

    Newly-appointed Assistant Professor Zach Hartwig’s mission is to use nuclear technology to benefit society and the environment.

    Making nuclear fusion a practical energy source is a complex challenge that will require diverse capabilities — like the scientific, engineering, communication, and leadership skills that Zach Hartwig has applied during almost a decade of doctoral and postdoc work at MIT’s Department of Nuclear Science and Engineering (NSE).

    Hartwig, who was recently named an NSE assistant professor, has helped develop a groundbreaking materials diagnostic system for the Alcator C-Mod fusion reactor and led the establishment of a new ion accelerator lab. He has also advocated for scientific research before a variety of audiences, and, with a team of other postdocs, has proposed a promising new strategy for fusion energy development.

    All these efforts align with NSE’s ongoing mission of using nuclear technology to benefit society and the environment, he says.

    “There’s a rising energy in the department today,” says Hartwig, who also holds a co-appointment at MIT’s Plasma Science and Fusion Center (PSFC) and an affiliation with the Laboratory for Nuclear Security and Policy. “A sense that, yes, we need to do research and train students, but also that it’s our responsibility to get beyond our walls and have a positive impact in the world.”

    Hartwig’s current focus is the compelling prospect of applying new-generation, high-temperature superconducting magnet technology in fusion reactors while developing innovative technology and funding frameworks that can accelerate fusion’s deployment onto the electric grid. The strategy centers on a faster-better-cheaper approach to technology development and an aggressive pursuit of net energy gain from controlled fusion, and it is at the heart of new directions in fusion energy research at NSE and PSFC. It was developed by the PSFC team of Hartwig, Dan Brunner, Bob Mumgaard, and Brandon Sorbom.

    Newly-available superconducting materials like REBCO (a single-crystal material composed of yttrium, barium, copper, oxygen and other elements) allow the creation of unprecedentedly-high-field magnets. They may enable smaller and less-expensive versions of venerable tokamak-type fusion reactors (like the Alcator C-Mod, which was shuttered last year), in part because a doubling of magnetic field strength produces a 16-fold increase in fusion power density. Hartwig says a fast-track high-field magnet development program, followed by the possible building of a compact, net-energy-gain tokamak in the next 5-10 years, would be a watershed in dispelling fusion’s reputation as being always in the future.

    “If and when we do that, fusion will ramp exponentially, just as fission did,” Hartwig says. “But we need to hit it in, say, 2025 or 2030, not 2080, if fusion is going to help mitigate the worst effects of climate change. We believe high-field REBCO magnets enable us to do just that.”

    Private funding, driven by the huge commercial opportunities of a safe, carbon-free, always-on energy source, could complement government support of fusion energy sciences. Hartwig points to comparable efforts in space exploration, cancer and brain research, oceanography, and other fields. He adds that the high-field magnet approach to fusion is a good fit — a transformational breakthrough that’s well-matched to investors seeking high-impact solutions to global climate change.

    “Much smaller reactors are cheaper and require less of an organization — they can be built by a university, and let us move faster and try more things,” he says. “And if it really doesn’t pan out, it’s better to find out quickly.”

    In any event, competencies in superconducting magnets have broad applicability in sectors like energy storage, magnetic resonance imaging, and maglev transportation. Niobium-titanium low-temperature superconducting magnets are being used in the recently-commissioned Ionetix Superconducting Proton Cyclotron, the centerpiece of the ion accelerator lab that Hartwig created with NSE and PSFC graduate students Sorbom, Leigh Ann Kesler, and Steve Jepeal. Hartwig says he formed the seeds of his new lab even as a student and postdoc: “We did have a vision; there was an underutilized space and some pre-existing grants, and we poured in elbow grease.”

    “It’s the first new cyclotron on campus in decades,” Hartwig says. “Accelerators are good scientific tools. They’re usually associated with high-energy physics, but they’re primarily an industrial tool for measuring and modifying materials properties.”

    The new accelerator, which sits alongside three older systems, provides higher-energy particles, allowing investigation of previously inaccessible reactions and phenomena. Top priorities are nuclear security and development of systems that can quickly and safely detect nuclear materials in freight containers, but the lab is also making new connections between NSE faculty, students and staff.

    “It’s centrally located, and brings together people from many different groups in the department,” Hartwig says. “There’s so much expertise, the accelerators have lots of possible applications, and we’re all tinkerers. I predicted four years ago that it would have visitors every day, and I was right — we should sell tickets.”

    That outlook reflects Hartwig’s appreciation of collegial teamwork, and of the research community in and around NSE, which includes facilities like the PSFC, the fission-oriented Nuclear Reactor Laboratory, the Center for Advanced Nuclear Energy Systems, and laboratories for materials, corrosion, magnets, and quantum technology.

    “That’s a lot of big facilities, and most don’t exist anywhere else,” he says. “Having all those capabilities at a university is probably unique in the world, and it creates a lot of opportunities, in fusion and other areas, for MIT to do what only MIT can do — put things together and be the fabric where innovation occurs.”

    See the full article here .

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  • richardmitnick 12:05 pm on May 31, 2017 Permalink | Reply
    Tags: , , Exploring elusive high-energy particles in an unusual metal, MIT, ,   

    From M.I.T.: “Exploring elusive high-energy particles in an unusual metal” 

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    May 30, 2017
    David L. Chandler

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    Researchers have observed a novel phenomenon in sheets of tantalum arsenide that mimics the behavior of theorized (but never observed) particles called Weyl fermions. Courtesy of the researchers

    Exotic metal displays behavior that could lead to new infrared detectors.

    Mid-infrared wavelengths of light are invisible to the eye but can be useful for a number of technologies, including night vision, thermal sensing, and environmental monitoring. Now, a new phenomenon in an unconventional metal, found by physicists at MIT and elsewhere, could provide a new way of making highly sensitive detectors for these elusive wavelengths. The phenomenon is closely related to a particle that has been predicted by high-energy physicists but never observed.

    Physicists group all the fundamental particles in nature into two categories, fermions and bosons, according to a property called spin. The fermions, in turn, have three types: Dirac, Majorana, and Weyl. Dirac fermions include the electrons in regular metals such as copper or gold. The other two are unconventional particles that can give rise to strange and fundamentally new physics, which potentially can be used to build more efficient circuits and other devices.

    The Weyl fermion was first theorized almost a century ago by German physicist Hermann Weyl. Even though its existence is posited as part of the equations that form the widely accepted Standard Model of subatomic physics, Weyl fermions have never actually been observed experimentally. The theory predicts that they should move at the speed of light, and, at the same time, spin about the direction of motion. They come in two varieties depending on whether their rotation around the direction of motion is clockwise or counterclockwise. This property is known as the handedness, or chirality, of Weyl fermions.

    Even though Weyl fermions have never been observed directly, researchers have recently observed a phenomenon that mimics essential aspects of their theorized properties, in a class of unconventional metals known as Weyl semimetals. One remaining challenge was to experimentally measure the chirality of these Weyl fermions, which evaded detection from most standard experimental techniques.

    In a paper published in the journal Nature Physics, an MIT team was able to measure Weyl fermion chirality by using circularly polarized light. This work was done by MIT postdocs Qiong Ma and Su-Yang Xu; physics professors Nuh Gedik, Pablo Jarillo-Herrero, and Patrick Lee; and eight other researchers at MIT and other universities in the U.S., China, and Singapore.

    See the full article here .

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  • richardmitnick 1:26 pm on May 19, 2017 Permalink | Reply
    Tags: , Making brain implants smaller could prolong their lifespan, , MIT   

    From MIT: “Making brain implants smaller could prolong their lifespan” 

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    May 16, 2017
    Anne Trafton

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    Professor Michael Cima and his colleagues are now designing brain implants that can not only deliver electrical stimulation but also record brain activity or deliver drugs to very targeted locations. Image: Christine Daniloff/MIT

    Thin fibers could be used to deliver drugs or electrical stimulation, with less damage to the brain.

    Many diseases, including Parkinson’s disease, can be treated with electrical stimulation from an electrode implanted in the brain. However, the electrodes can produce scarring, which diminishes their effectiveness and can necessitate additional surgeries to replace them.

    MIT researchers have now demonstrated that making these electrodes much smaller can essentially eliminate this scarring, potentially allowing the devices to remain in the brain for much longer.

    “What we’re doing is changing the scale and making the procedure less invasive,” says Michael Cima, the David H. Koch Professor of Engineering in the Department of Materials Science and Engineering, a member of MIT’s Koch Institute for Integrative Cancer Research, and the senior author of the study, which appears in the May 16 issue of Scientific Reports.

    Cima and his colleagues are now designing brain implants that can not only deliver electrical stimulation but also record brain activity or deliver drugs to very targeted locations.

    The paper’s lead author is former MIT graduate student Kevin Spencer. Other authors are former postdoc Jay Sy, graduate student Khalil Ramadi, Institute Professor Ann Graybiel, and David H. Koch Institute Professor Robert Langer.

    See the full article here .
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  • richardmitnick 4:29 pm on May 18, 2017 Permalink | Reply
    Tags: , Lung adenocarcinoma, Lung cancer, , MIT,   

    From MIT: “Biologists identify key step in lung cancer evolution” 

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    May 10, 2017
    Anne Trafton

    1
    MIT researchers have found that lung tumors such as this one contain stem-cell-like cells that drive tumor aggression. In this image, those cells are tagged with a green fluorescent protein.
    Image: Tuomas Tammela

    Blocking the transition to a more aggressive state could offer a new treatment strategy.

    [My wife of 53 years died from lung cancer, or the immunotherapy she received to treat it. So this is very personal and difficult for me.]

    Lung adenocarcinoma, an aggressive form of cancer that accounts for about 40 percent of U.S. lung cancer cases, is believed to arise from benign tumors known as adenomas.

    MIT biologists have now identified a major switch that occurs as adenomas transition to adenocarcinomas in a mouse model of lung cancer. They’ve also discovered that blocking this switch prevents the tumors from becoming more aggressive. Drugs that interfere with this switch may thus be useful in treating early-stage lung cancers, the researchers say.

    “Understanding the molecular pathways that get activated as a tumor transitions from a benign state to a malignant one has important implications for treatment. These findings also suggests methods to prevent or interfere with the onset of advanced disease,” says Tyler Jacks, director of MIT’s Koch Institute for Integrative Cancer Research and the study’s senior author.

    The switch occurs when a small percentage of cells in the tumor begin acting like stem cells, allowing them to give rise to unlimited populations of new cancer cells.

    “It seems that the stem cells are the engine of tumor growth. They’re endowed with very robust proliferative potential, and they give rise to other cancer cells and also to more stem-like cells,” says Tuomas Tammela, a postdoc at the Koch Institute and lead author of the paper, which appears in the May 10 online edition of Nature.

    Tumor stem cells

    In this study, the researchers focused on the role of a cell signaling pathway known as Wnt. This pathway is usually turned on only during embryonic development, but it is also active in small populations of adult stem cells that can regenerate specific tissues such as the lining of the intestine.

    One of the Wnt pathway’s major roles is maintaining cells in a stem-cell-like state, so the MIT team suspected that Wnt might be involved in the rapid proliferation that occurs when early-stage tumors become adenocarcinomas.

    The researchers explored this question in mice that are genetically programmed to develop lung adenomas that usually progress to adenocarcinoma. In these mice, they found that Wnt signaling is not active in adenomas, but during the transition, about 5 to 10 percent of the tumor cells turn on the Wnt pathway. These cells then act as an endless pool of new cancer cells.

    In addition, about 30 to 40 percent of the tumor cells begin to produce chemical signals that create a “niche,” a local environment that is necessary to maintain cells in a stem-cell-like state.

    “If you take a stem cell out of that microenvironment, it rapidly loses its properties of stem-ness,” Tammela says. “You have one cell type that forms the niche, and then you have another cell type that’s receiving the niche cues and behaves like a stem cell.”

    While Wnt has been found to drive tumor formation in some other cancers, including colon cancer, this study points to a new kind of role for it in lung cancer and possibly other cancers such as pancreatic cancer.

    “What’s new about this finding is that the pathway is not a driver, but it modifies the characteristics of the cancer cells. It qualitatively changes the way cancer cells behave,” Tammela says.

    “It’s a very nice paper that points to the influence of the microenvironment in tumor growth and shows that the microenvironment includes factors secreted by a subset of tumor cells,” says Frederic de Sauvage, vice president for molecular oncology research at Genentech, who was not involved in the study.

    Targeting Wnt

    When the researchers gave the mice a drug that interferes with Wnt proteins, they found that the tumors stopped growing, and the mice lived 50 percent longer. Furthermore, when these treated tumor cells were implanted into another animal, they failed to generate new tumors.

    The researchers also analyzed human lung adenocarcinoma samples and found that 70 percent of the tumors showed Wnt activation and 80 percent had niche cells that stimulate Wnt activity. These findings suggest it could be worthwhile to test Wnt inhibitors in early-stage lung cancer patients, the researchers say.

    They are also working on ways to deliver Wnt inhibitors in a more targeted fashion, to avoid some of the side effects caused by the drugs. Another possible way to avoid side effects may be to develop more specific inhibitors that target only the Wnt proteins that are active in lung adenocarcinomas. The Wnt inhibitor that the researchers used in this study, which is now in clinical trials to treat other types of cancer, targets all 19 of the Wnt proteins.

    The research was funded by the Janssen Pharmaceuticals-Koch Institute Transcend Program, the Lung Cancer Research Foundation, the Howard Hughes Medical Institute, and the Cancer Center Support grant from the National Cancer Institute.

    See the full article here .
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  • richardmitnick 3:48 pm on May 18, 2017 Permalink | Reply
    Tags: , CLEARN, , MIT,   

    From MIT: “Teaching robots to teach other robots” 

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    May 10, 2017
    Adam Conner-Simons | CSAIL

    1
    MIT doctoral candidate Claudia Pérez-D’Arpino discusses her work teaching the Optimus robot to perform various tasks, including picking up a bottle. Photo: Jason Dorfman/MIT CSAIL

    CSAIL approach allows robots to learn a wider range of tasks using some basic knowledge and a single demo.

    Most robots are programmed using one of two methods: learning from demonstration, in which they watch a task being done and then replicate it, or via motion-planning techniques such as optimization or sampling, which require a programmer to explicitly specify a task’s goals and constraints.

    Both methods have drawbacks. Robots that learn from demonstration can’t easily transfer one skill they’ve learned to another situation and remain accurate. On the other hand, motion planning systems that use sampling or optimization can adapt to these changes but are time-consuming, since they usually have to be hand-coded by expert programmers.

    Researchers from MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) have recently developed a system that aims to bridge the two techniques: C-LEARN, which allows noncoders to teach robots a range of tasks simply by providing some information about how objects are typically manipulated and then showing the robot a single demo of the task.

    Importantly, this enables users to teach robots skills that can be automatically transferred to other robots that have different ways of moving — a key time- and cost-saving measure for companies that want a range of robots to perform similar actions.

    “By combining the intuitiveness of learning from demonstration with the precision of motion-planning algorithms, this approach can help robots do new types of tasks that they haven’t been able to learn before, like multistep assembly using both of their arms,” says Claudia Pérez-D’Arpino, a PhD student who wrote a paper on C-LEARN with MIT Professor Julie Shah.

    The team tested the system on Optimus, a new two-armed robot designed for bomb disposal that they programmed to perform tasks such as opening doors, transporting objects, and extracting objects from containers. In simulations they showed that Optimus’ learned skills could be seamlessly transferred to Atlas, CSAIL’s 6-foot-tall, 400-pound humanoid robot.

    A paper describing C-LEARN was recently accepted to the IEEE International Conference on Robotics and Automation (ICRA), which takes place May 29 to June 3 in Singapore.

    How it works

    With C-LEARN the user first gives the robot a knowledge base of information on how to reach and grasp various objects that have different constraints. (The C in C-LEARN stands for “constraints.”) For example, a tire and a steering wheel have similar shapes, but to attach them to a car, the robot has to configure its arms differently to move them. The knowledge base contains the information needed for the robot to do that.

    The operator then uses a 3-D interface to show the robot a single demonstration of the specific task, which is represented by a sequence of relevant moments known as “keyframes.” By matching these keyframes to the different situations in the knowledge base, the robot can automatically suggest motion plans for the operator to approve or edit as needed.

    “This approach is actually very similar to how humans learn in terms of seeing how something’s done and connecting it to what we already know about the world,” says Pérez-D’Arpino. “We can’t magically learn from a single demonstration, so we take new information and match it to previous knowledge about our environment.”

    One challenge was that existing constraints that could be learned from demonstrations weren’t accurate enough to enable robots to precisely manipulate objects. To overcome that, the researchers developed constraints inspired by computer-aided design (CAD) programs that can tell the robot if its hands should be parallel or perpendicular to the objects it is interacting with.

    The team also showed that the robot performed even better when it collaborated with humans. While the robot successfully executed tasks 87.5 percent of the time on its own, it did so 100 percent of the time when it had an operator that could correct minor errors related to the robot’s occasional inaccurate sensor measurements.

    “Having a knowledge base is fairly common, but what’s not common is integrating it with learning from demonstration,” says Dmitry Berenson, an assistant professor at the University of Michigan’s Electrical Engineering and Computer Science Department. “That’s very helpful, because if you are dealing with the same objects over and over again, you don’t want to then have to start from scratch to teach the robot every new task.”

    Applications

    The system is part of a larger wave of research focused on making learning-from-demonstration approaches more adaptive. If you’re a robot that has learned to take an object out of a tube from a demonstration, you might not be able to do it if there’s an obstacle in the way that requires you to move your arm differently. However, a robot trained with C-LEARN can do this, because it does not learn one specific way to perform the action.

    “It’s good for the field that we’re moving away from directly imitating motion, toward actually trying to infer the principles behind the motion,” Berenson says. “By using these learned constraints in a motion planner, we can make systems that are far more flexible than those which just try to mimic what’s being demonstrated”

    Shah says that advanced LfD methods could prove important in time-sensitive scenarios such as bomb disposal and disaster response, where robots are currently tele-operated at the level of individual joint movements.

    “Something as simple as picking up a box could take 20-30 minutes, which is significant for an emergency situation,” says Pérez-D’Arpino.

    C-LEARN can’t yet handle certain advanced tasks, such as avoiding collisions or planning for different step sequences for a given task. But the team is hopeful that incorporating more insights from human learning will give robots an even wider range of physical capabilities.

    “Traditional programming of robots in real-world scenarios is difficult, tedious, and requires a lot of domain knowledge,” says Shah. “It would be much more effective if we could train them more like how we train people: by giving them some basic knowledge and a single demonstration. This is an exciting step toward teaching robots to perform complex multiarm and multistep tasks necessary for assembly manufacturing and ship or aircraft maintenance.”

    See the full article here .

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  • richardmitnick 2:46 pm on May 18, 2017 Permalink | Reply
    Tags: MIT, , NASA Viking Lander, Rivers on three worlds tell different tales   

    From MIT: “Rivers on three worlds tell different tales” 

    MIT News

    MIT Widget

    MIT News

    May 18, 2017
    Jennifer Chu

    1
    Left to right: River networks on Mars, Earth, and Titan. Researchers report that Titan, like Mars but unlike Earth, has not undergone any active plate tectonics in its recent past. Image: Benjamin Black/NASA/Visible Earth/JPL/Cassini RADAR team. Adapted from images from NASA Viking, NASA/Visible Earth, and NASA/JPL/Cassini RADAR team

    NASA/Viking 1 Lander

    NASA/ESA/ASI Cassini-Huygens Spacecraft

    The environment on Titan, Saturn’s largest moon, may seem surprisingly familiar: Clouds condense and rain down on the surface, feeding rivers that flow into oceans and lakes. Outside of Earth, Titan is the only other planetary body in the solar system with actively flowing rivers, though they’re fed by liquid methane instead of water. Long ago, Mars also hosted rivers, which scoured valleys across its now-arid surface.

    Now MIT scientists have found that despite these similarities, the origins of topography, or surface elevations, on Mars and Titan are very different from that on Earth.

    In a paper published today in Science, the researchers report that Titan, like Mars but unlike Earth, has not undergone any active plate tectonics in its recent past. The upheaval of mountains by plate tectonics deflects the paths that rivers take. The team found that this telltale signature was missing from river networks on Mars and Titan.

    “While the processes that created Titan’s topography are still enigmatic, this rules out some of the mechanisms we’re most familiar with on Earth,” says lead author Benjamin Black, formerly an MIT graduate student and now an assistant professor at the City College of New York.

    Instead, the authors suggest Titan’s topography may grow through processes like changes in the thickness of the moon’s icy crust, due to tides from Saturn.

    The study also sheds some light on the evolution of the landscape on Mars, which once harbored a huge ocean and rivers of water. The MIT team provides evidence that the major features of Martian topography formed very early in the history of the planet, influencing the paths of younger river systems, even as volcanic eruptions and asteroid impacts scarred the planet’s surface.

    “It’s remarkable that there are three worlds in the solar system where flowing rivers have carved into the landscape, either presently or in the past,” says Taylor Perron, associate professor of geology in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS). “There’s this amazing opportunity to use the landforms the rivers have created to learn how the histories of these worlds are different.”

    Perron and Black’s co-authors include former MIT undergraduate Elizabeth Bailey and researchers from the University of California at Berkeley, the University of California at Santa Cruz, and Stanford University.

    Fuzzy flows

    Since 2004, NASA’s Cassini spacecraft has been circling Saturn and sending back to Earth stunning images of the planet’s rings and moons. Images of Titan’s surface have given scientists a first view of the moon’s river valleys, rolling sand dunes, and active weather patterns. Cassini has also made rough measurements of Titan’s topography in some locations, though these measurements are much coarser in resolution.

    Perron and Black wondered whether they might refine their view of Titan’s topography by applying what is known about the topography on Earth and Mars, and how their rivers have evolved.

    For instance, on Earth, the process of plate tectonics has continuously reshaped the landscape, pushing mountain ranges up between colliding continental plates, and opening ocean basins as landmasses slowly pull apart. Rivers, therefore, are constantly adapting to changes in topography, sidestepping around growing mountain ranges to reach the ocean.

    Mars, on the other hand, is thought to have been shaped mostly during the period of primordial accretion and the so-called Late Heavy Bombardment, when asteroids carved out massive impact basins and pushed up huge volcanoes.

    Scientists now have well-resolved maps of river networks and topography on both Earth and Mars, along with a growing understanding of their respective histories. Perron and Black used this foundation to gain insight into Titan’s topographic history.

    “We know something about rivers, and something about topography, and we expect that rivers are interacting with topography as it evolves,” Black says. “Our goal was to use those pieces to crack the code of what formed the topography in the first place.”

    Conforming with topography

    The team first compiled a map of river networks for Earth, Mars, and Titan. Such maps were previously made by others for Earth and Mars; Black generated a river map for Titan using images taken by Cassini. For all three maps, the researchers marked the direction each river appeared to flow.

    They then compared topographic maps for all three planetary bodies, at varying degrees of resolution. Maps of Earth are sharp in detail, as are those for Mars, showing mountain peaks and impact basins in high relief. By contrast, due to Titan’s thick, hazy atmosphere, the global map of Titan’s topography is extremely fuzzy, showing only the broadest features.

    In order to make direct comparisons between topographies, the researchers dialed down the resolution of maps for Earth and Mars, to match the resolution available for Titan. They then superimposed maps of each planetary body’s river networks, onto their respective topographies, and marked every river that appeared to flow downhill.

    Of course, rivers only flow downhill. But the team observed that rivers might appear to flow uphill, simply because a map at low resolution may not capture finer details such as mountain ranges which would divert a river’s flow.

    When the researchers tallied the percentage of rivers on Titan that appeared to flow downhill, the number more closely matched with Mars. They also compared what they called “topographic conformity” — the degree of divergence between a topography’s slope and the direction of a river’s flow. Here too, they found that Titan resembled Mars over Earth.

    “One prediction we can make is that, when we eventually get more refined topographic maps of Titan, we will see topography that looks more like Mars than Earth,” Perron says. “Titan might have broad-scale highs and lows, which might have formed some time ago, and the rivers have been eroding into that topography ever since, as opposed to having new mountain ranges popping up all the time, with rivers constantly fighting against them.”

    Filling in a picture

    One last question the researchers looked to answer was how cratering due to asteroid impacts on Mars has reshaped its topography.

    Black used a simulation that the group previously developed, to model river erosion on Mars with different impact cratering histories. He found that the pattern of river networks on Mars today limits the extent to which cratering has remodeled the surface of Mars. This suggests that the biggest impact craters formed very early in Mars’ history, and that later pummeling by asteroids mostly dented and dinged the surface.

    As Cassini’s mission is scheduled to come to an end in September, Perron says further investigation of Titan’s surface will help to guide future missions to the distant moon.

    “Any way of filling in the details of what Titan’s surface is like, beyond what we can see directly in the images and topography Cassini has collected, will be valuable for planning a return,” Perron says.

    This research was funded, in part, by NASA.

    See the full article here .

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  • richardmitnick 2:11 pm on May 14, 2017 Permalink | Reply
    Tags: , , , Medscape, MIT, , WCG Outsmart Ebola Together   

    From Medscape via Broad: Women in Stem- “Outbreaks, Evolution, and Rock ‘n’ Roll: Topol Talks to Pardis Sabeti” 

    Broad Institute

    Broad Institute

    1

    Medscape

    May 10, 2017
    Eric J. Topol, MD

    3
    Pardis Sabeti

    Eric J. Topol, MD: Hello. I am Eric Topol, editor-in-chief of Medscape. I have the special privilege of having a conversation with Pardis Sabeti. She is an extraordinary scientist and physician at the Broad Institute at Harvard Medical School and MIT. We are going to talk about the arc of her life and career, beginning when she moved here at age 2 from Tehran.

    Pardis Sabeti, MD, DPhil: Yes. We came to the United States around the time of the Iranian revolution and had refugee status here. Then we moved to Hawaii, New Jersey, Georgia, and Florida, and we settled in Florida.

    Dr Topol: At one point you were not sure whether you were going to own a flower shop, be a novelist, or become a doctor. Is that right?

    Dr Sabeti: That was when I was about 6 years old. I liked flowers a lot, so I thought, “This seems like the life.” As a kid, I liked to write. As an immigrant and as a child of revolution, my dad amused himself by saying, “You can be anything you want to be in the world: a lawyer or a doctor.” My sister became a lawyer and I became a doctor, but neither of us practice.

    Dr Topol: Music has been a big part of your life. When did that become rooted?

    Dr Sabeti: That was not until graduate school. I have liked music my whole life and played a little piano as a kid. I went to concerts all the time. That was how I enjoyed spending my time. When I was in grad school, I had two American friends and we were in England together. They would play “fantasy band” all the time and make up band names and that kind of stuff. One night I said, “Why do you keep fantasy-banding? Why not just start a band?” They said they at least had to have a rhythm section, so the next day I bought a bass and that started my journey.

    Dr Topol: These days, you are a lead singer and writer for a rock band. How often do you get involved with that?

    Dr Sabeti: It wanes and waxes. It’s not very conducive to faculty life. I dropped it for a while and then I had an accident and picked it up again. Music is great, because every once in a while your soul just wants to speak and you have an opportunity to do it. It’s pretty sporadic, but I have been writing some music recently.

    Dr Topol: Somehow or other, you landed at MIT.

    Dr Sabeti: In the 6th grade, the idea of going to MIT got sparked. My math teacher showed us a 270 competition: The MIT mechanical engineering department has a contest in which everyone builds robots that compete against each other. I saw that video as a kid and thought, “I need to be there.” I was locked onto MIT as my dream school since then.

    Dr Topol: You also became a Rhodes Scholar and went to Oxford.

    Dr Sabeti: It was a bizarre experience right after college to be in this wonderland that was Oxford, and a lot of existential crises happened right after college. It was a very informative and great experience.

    Dr Topol: Were you already starting to get into the whole selection, mutation, and evolutionary biology by then?

    Dr Sabeti: No. I think that is what made that happen. I had gone to MIT and I loved all the engineering, but I still thought that I was supposed to be a doctor. I had intended to go to medical school, but I got this scholarship on a lark. I was planning to go to medical school when I came back. Along the way, somehow, I ended up getting a PhD. It was an interesting experience there. They had a shorter PhD track. That was when I started doing that work, and it changed the direction of my life.

    In the Middle of an Outbreak

    Dr Topol: And then you went to medical school—a big commitment. When you started your career, did you know that you were going to be leading the charge to do genomic epidemiology of Ebola and Zika?

    Dr Sabeti: Definitely not. Because I never intended to be a scientist, I didn’t have a very specific path for what I wanted to do. I feel like I am on a scavenger hunt; I don’t know exactly where it’s going, but this path has captured my attention for some time.

    Dr Topol: This is quite a hunt. Just what you did with Ebola—you were named a Time “Person of the Year” in 2014 and one of the 100 most influential people in the world. You went to West Africa with folks in your lab, and many other people you work with, to try to get the knowledge that was needed to titrate the horrendous Ebola epidemic. Can you tell us about that?

    Dr Sabeti: Sure. For one thing, I am just a bit player. At the end of the day, the Ebola fighters were recognized for the work that we all did collectively. I was privileged to be one of the people who were named as an example, but it was a collective effort. To us, the seemingly small part that we played was that we naturally come from the genomics world—I cut my teeth on the Human Genome Project—where sharing data and an open feeling about science was just a given.

    This is an outbreak that we found ourselves in the middle of because it came to the site where we were working in Africa. As we were trying to do what we could to help our collaborators and partners there, and to get attention, we started publishing science on this. We started releasing our data to the lab. What was interesting is that we decided we didn’t care about getting recognition; we just wanted to get the data out to the world. Paradoxically, that is what got us attention. It was apparently unusual to share data openly as soon as you generated it. It became a call to the community.

    Dr Topol: You were putting your lives on the line to do this work. What was that like?

    Dr Sabeti: To be honest, as a scientist, that is the risk you take. We were working on Lassa fever for some time. I have been quarantined before. We take risks, but they are very measured, calculated risks. Fundamentally, in all cases, it was the clinicians who became infected. We saw that across the board in the outbreak. As the researchers, we work in a very contained environment and we can isolate things very well. We are really in the service of the clinicians. We take risks, but for us, there was more risk of being in a car crash than being infected with Ebola. We were honored to be there to support them.

    Dr Topol: More recently, you have been involved with the Zika virus story. Where do we stand with that?

    Dr Sabeti: Zika is different. Ebola was a rapidly escalating outbreak. It was one of those viruses that can transmit from human to human with very acute infections and a very high fatality rate. It was a frightening event. Zika is less fatal. It does not transmit as easily. It usually involves mosquitoes. But it is a more challenging virus to battle; it’s more widespread, and mosquitoes are hard to manage. The virus hides itself a little at low concentrations in the blood for short periods of time, so the diagnosis is challenging. But it becomes really important because of the effects it can have on pregnancy and on children born to mothers who have Zika. Zika causes a visceral reaction in all of us because it affects a vulnerable population that we all care about.

    Please Play With Our Data

    Dr Topol: In 2015 you gave a TED Talk on how we are going to deal with the next deadly virus. Can you summarize what you talked about at the time?

    Dr Sabeti: That was in the middle of the Ebola outbreak. I had been asked to give a talk at TEDWomen. I just discussed what was on my mind at the time. I had not really thought out exactly what the message would be, and I did not know, necessarily, that it would be posted online. In fact, I sang during my talk. It was good in the room, but they wanted to cut it out and make it the right length [for TED Talks online]. I just had fun with it. The message was about outbreaks and how frightening they are. But it’s a war that we can win—but that we win by collaboration. It is very different from other types of threats to humanity. That was what I felt—the power of human capacity and love to overcome these kinds of challenges.

    See the full article here .

    You can Help Stamp Out EBOLA.

    This WCG project runs at Scripps Institute

    Scripps

    Outsmart Ebola Together

    Visit World Community Grid (WCG). Download and install the BOINC software on which it runs. Attach to the Outsmart Ebola Together project. This will allow WCG to use your computer’s free CPU cycles to process computational data for the project.

    While you are at WCG and BOINC, check out the other very worthwhile projects running on this software. All project results are “open source”, free for the use of scientists world while to advance health and other issues of mankind.

    YOU CAN HELP FIND A CURE FOR THE ZIKA VIRUS.

    There is a new project at World Community Grid [WCG] called OpenZika.
    Zika
    Zika depiction. Image copyright John Liebler, http://www.ArtoftheCell.com
    Rutgers Open Zika

    WCG runs on your home computer or tablet on software from Berkeley Open Infrastructure for Network Computing [BOINC]. Many other scientific projects run on BOINC software.Visit WCG or BOINC, download and install the software, then at WCG attach to the OpenZika project. You will be joining tens of thousands of other “crunchers” processing computational data and saving the scientists literally thousands of hours of work at no real cost to you.

    This project is directed by Dr. Alexander Perryman a senior researcher in the Freundlich lab, with extensive training in developing and applying computational methods in drug discovery and in the biochemical mechanisms of multi-drug-resistance in infectious diseases.

    1
    Dr. Alex Perryman, Rutgers New Jersey Medical School

    He is a member of the Center for Emerging & Re-emerging Pathogens, in the Department of Pharmacology, Physiology, and Neuroscience, at the Rutgers University, New Jersey Medical School. Previously, he was a Research Associate in Prof. Arthur J. Olson’s lab at The Scripps Research Institute (TSRI), where he ran the day-to-day operations of the FightAIDS@Home project, the largest computational drug discovery project devoted to HIV/AIDS, which also runs on WCG. While in the Olson lab, he also designed, led, and ran the largest computational drug discovery project ever performed against malaria, the GO Fight Against Malaria project, also on WCG.

    Rutgers smaller

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    The Eli and Edythe L. Broad Institute of Harvard and MIT is founded on two core beliefs:

    This generation has a historic opportunity and responsibility to transform medicine by using systematic approaches in the biological sciences to dramatically accelerate the understanding and treatment of disease.
    To fulfill this mission, we need new kinds of research institutions, with a deeply collaborative spirit across disciplines and organizations, and having the capacity to tackle ambitious challenges.

    The Broad Institute is essentially an “experiment” in a new way of doing science, empowering this generation of researchers to:

    Act nimbly. Encouraging creativity often means moving quickly, and taking risks on new approaches and structures that often defy conventional wisdom.
    Work boldly. Meeting the biomedical challenges of this generation requires the capacity to mount projects at any scale — from a single individual to teams of hundreds of scientists.
    Share openly. Seizing scientific opportunities requires creating methods, tools and massive data sets — and making them available to the entire scientific community to rapidly accelerate biomedical advancement.
    Reach globally. Biomedicine should address the medical challenges of the entire world, not just advanced economies, and include scientists in developing countries as equal partners whose knowledge and experience are critical to driving progress.

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  • richardmitnick 1:19 pm on May 5, 2017 Permalink | Reply
    Tags: MIT, , Sandwiched between superconductors graphene adopts exotic electronic states   

    From MIT: “Sandwiched between superconductors, graphene adopts exotic electronic states” 

    MIT News

    MIT Widget

    MIT News

    May 4, 2017
    Jennifer Chu

    1
    MIT physicists have found that a flake of graphene, when brought in close proximity with two superconducting materials, can inherit some of those materials’ superconducting qualities. As graphene is sandwiched between superconductors, its electronic state changes dramatically, even at its center. Pictured is the experimental concept and device schematic.

    In normal conductive materials such as silver and copper, electric current flows with varying degrees of resistance, in the form of individual electrons that ping-pong off defects, dissipating energy as they go. Superconductors, by contrast, are so named for their remarkable ability to conduct electricity without resistance, by means of electrons that pair up and move through a material as one, generating no friction.

    Now MIT physicists have found that a flake of graphene, when brought in close proximity with two superconducting materials, can inherit some of those materials’ superconducting qualities. As graphene is sandwiched between superconductors, its electronic state changes dramatically, even at its center.

    The researchers found that graphene’s electrons, formerly behaving as individual, scattering particles, instead pair up in “Andreev states” — a fundamental electronic configuration that allows a conventional, nonsuperconducting material to carry a “supercurrent,” an electric current that flows without dissipating energy.

    Their findings, published this week in Nature Physics, are the first investigation of Andreev states due to superconductivity’s “proximity effect” in a two-dimensional material such as graphene.

    Down the road, the researchers’ graphene platform may be used to explore exotic particles, such as Majorana fermions, which are thought to arise from Andreev states and may be key particles for building powerful, error-proof quantum computers.

    “There is a huge effort in the condensed physics community to look for exotic quantum electronic states,” says lead author Landry Bretheau, a postdoc in MIT’s Department of Physics. “In particular, new particles called Majorana fermions are predicted to emerge in graphene that is connected to superconducting electrodes and exposed to large magnetic fields. Our experiment is promising, as we are unifying some of these ingredients.”

    Landry’s MIT co-authors are postdoc Joel I-Jan Wang, visiting student Riccardo Pisoni, and associate professor of physics Pablo Jarillo-Herrero, along with Kenji Watanabe and Takashi Taniguchi of the National Institute for Materials Science, in Japan.

    The superconducting proximity effect

    In 1962, the British physicist Brian David Josephson predicted that two superconductors sandwiching a nonsuperconducting layer between them could sustain a supercurrent of electron pairs, without any external voltage.

    As a whole, the supercurrent associated with the Josephson effect has been measured in numerous experiments. But Andreev states — considered the microscopic building blocks of a supercurrent — have been observed only in a handful of systems, such as silver wires, and never in a two-dimensional material.

    Bretheau, Wang, and Jarillo-Herrero tackled this issue by using graphene — an ultrathin sheet of interlinked carbon atoms — as the nonsuperconducting material. Graphene, as Bretheau explains, is an extremely “clean” system, exhibiting very little scattering of electrons. Graphene’s extended, atomic configuration also enables scientists to measure graphene’s electronic Andreev states as the material comes in contact with superconductors. Scientists can also control the density of electrons in graphene and investigate how it affects the superconducting proximity effect.

    The researchers exfoliated a very thin flake of graphene, just a few hundred nanometers wide, from a larger chunk of graphite, and placed the flake on a small platform made from a crystal of boron nitride overlaying a sheet of graphite. On either end of the graphene flake, they placed an electrode made from aluminum, which behaves as a superconductor at low temperatures. They then placed the entire structure in a dilution refrigerator and lowered the temperature to 20 millikelvin — well within aluminum’s superconducting range.

    “Frustrated” states

    In their experiments, the researchers varied the magnitude of the supercurrent flowing between the superconductors by applying a changing magnetic field to the entire structure. They also applied an external voltage directly to graphene, to vary the number of electrons in the material.

    Under these changing conditions, the team measured the graphene’s density of electronic states while the flake was in contact with both aluminum superconductors. Using tunneling spectroscopy, a common technique that measures the density of electronic states in a conductive sample, the researchers were able to probe the graphene’s central region to see whether the superconductors had any effect, even in areas where they weren’t physically touching the graphene.

    The measurements indicated that graphene’s electrons, which normally act as individual particles, were pairing up, though in “frustrated” configurations, with energies dependent on magnetic field.

    “Electrons in a superconductor dance harmoniously in pairs, like a ballet, but the choreography in the left and right superconductors can be different,” Bretheau says. “Pairs in the central graphene are frustrated as they try to satisfy both ways of dancing. These frustrated pairs are what physicists know as Andreev states; they are carrying the supercurrent.”

    Bretheau and Wang found Andreev states vary their energy in response to a changing magnetic field. Andreev states are more pronounced when graphene has a higher density of electrons and there is a stronger supercurrent running between electrodes.

    “[The superconductors] are actually giving graphene some superconducting qualities,” Bretheau says. “We found these electrons can be dramatically affected by superconductors.”

    While the researchers carried out their experiments under low magnetic fields, they say their platform may be a starting point for exploring the more exotic Majorana fermions that should appear under high magnetic fields.

    “There are proposals for how to use Majorana fermions to build powerful quantum computers,” Bretheau says. “These particles could be the elementary brick of topological quantum computers, with very strong protection against errors. Our work is an initial step in this direction.”

    This work was supported, in part, by the U.S. Department of Energy and the Gordon and Betty Moore Foundation.

    See the full article here .

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